Quote:
Originally Posted by Harri Pihl
For 600lbs increase from 9680lbs to 10280lbs in the case of the P-51B causes 1,48km/h speed reduction for max speed at sea level. The parameters being 352mph at sealevel and, 1580hp (67") and 120kp exhaust thrust, prop efficiency 80% and value of the e being 0,8. Calculated Cd0 being 0,02054.
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Your specific references for each claim you just made for the P-51B?
For example "e" is derived empirically, because the effect of spanwise lift distribution, increase in trim drag and the increases in all forms of drag on the airframe. .8 is a good rule of thumb for conservative preliminary design purposes - but only that unless you have test results?
Ditto prop efficiency. .8 to .85 are good Prelim Design numers. So where would point me to .8 as being correct for the P-51B?..
Cd0 = .02054? and your source is? That is higher than the Ames wind tunnel model with real airframe.
Having said that, how do you arrive at approximately 1mph delta for a 6% weight increase? What math are you using?